A conventional projection TV includes a structure shown in FIG. 1. More specifically, a projected image from an image projection tube 1 is reflected by a mirror 2 and then focused onto a screen plate 3. As shown in FIG. 2(a), the screen plate 3 is comprised of a Fresnel lens 4, a diffusion plate 5 and a protecting plate 6. As shown in FIGS. 2(b) and 2(c), the diffusion plate 5 includes a plurality of angle protrusions 7 which are formed in parallel with each other and which extend in the longitudinal direction of the diffusion plate 5. The protecting plate 6 is formed of a transparent plastic plate.
In addition to a diffusion function, the angle protrusions 7 of the diffusion plate 5 have a lens effect by which the projected image is zoomed in the lateral direction of the diffusion plate 5. The protecting plate 6 is originally provided to protect a diffusion surface of the diffusion plate 5 from scratch or dust. However, since the protecting plate 6 is the transparent plate having a flat surface, surrounding lighting equipment tends to project with the eventual image, resulting in visually unclear image. Thus, a surface of the protecting plate 6 exposed outside is desirable to be a frosted surface having a microscopic irregularity. A surface of the diffusion plate 5 opposite to the diffusion surface thereof may also be formed in a frosted surface to expose outside without providing the protecting plate 6 separately
In view of cost and weight, it is desirable to mold the Fresnel lens 4, the diffusion plate 5 and the protecting plate 6, all of which are components of such a screen plate 3, from a plastic material. However, it is not easy to mold a thin-plate article having a microscopic irregular pattern on the surface thereof from a plastic material.